In a 3-quart pot set over high heat, add the water, salt, garlic, onions and herb bundle and bring to a boil. Reduce the heat to medium and add the steak. Simmer until the meat turns tender, about 1 hour.
Set a 12-inch skillet set over medium heat and film with oil. Add the onion slices and cook for 2 to 3 minutes. Remove meat from pot and cut into 1/2-inch cubes, then add to the skillet with the onions and cook until the meat and onions are browned, abut 7 to 8 minutes.
Add the cheese and epazote leaves and stir to combine. Scoop the mixture into warm corn tortillas and add a few dashes of hot sauce.